This invention relates to an ink jet recording apparatus in which ink is supplied from an ink container placed on a housing to a record head mounted on a carriage though a tube, and more particularly to an ink supply system, a sub-tank unit adapted thereto, and operation techniques associated therewith.
An ink jet recording apparatus used for printing a large number of pages adopts a structure wherein an ink container such as a cassette is placed on a housing and is connected to a sub-tank unit mounted on a carriage through an ink supply tube for supplying ink consumed for print to a record head through the sub-tank unit, for example, as shown in JP-B-4-43785.
Such a structure makes it possible to remarkably prevent change in ink pressure caused by stretching and bending the tube as the carriage moves, thereby maintaining print quality.
On the other hand, to improve the print quality in a color print mode, a recording apparatus using different types of ink to produce light and shade in the same color group involves the following problem: As the ink types increase, the number of ink tubes increases and for the necessity for guiding the tubes so as to be able to follow a movement of a carriage, the structure for routing the tubes becomes complicated and receives restrictions and moreover the elasticity and rigidity of the tubes affect motion of the carriage, making it difficult to execute print at high speed.
To solve such a problem, JP-A-10-244685 proposes a recording apparatus comprising a sub-tank unit mounted on a carriage for supplying ink to an ink jet record head, and an ink replenishment unit connected to an ink cartridge placed on a housing by a duct and detachably connectable to the sub-tank unit.
According to the recording apparatus, the carriage is moved in a disconnection state from the duct of a tube, etc., during printing, and connection to the duct is made only when it becomes necessary to replenish the sub-tank unit with ink. Therefore, it is not necessary to cause the tube forming the duct to follow the carriage movement, routing of the tube can be simplified, and expanding or contracting of the tube is not involved in the carriage movement, so that the carriage can be moved at high speed, making it possible to execute print at high speed.
However, ink supply to the sub-tank unit from the ink cartridge placed on the housing relies on slight negative pressure caused by an expansion force produced by an elastic member preliminarily built in the sub-tank unit, thus if air accumulates in the sub-tank unit as the sub-tank unit is replenished with ink a large number of times, the negative pressure lowers, the replenishment amount lowers, and it takes time in replenishing the sub-tank unit with ink; this is a problem.
To solve such a problem, JP-A-9-29991 proposes a system wherein an ink full sensor and an ink empty sensor are contained in a sub-tank unit, an ink injection port incorporating a projection member for pushing and opening a valve on the side of an ink supply nozzle is provided for injection ink from an ink replenishment tank positioned in an upper part, and replenishment with ink is stopped based on a signal from the ink full sensor.
This system involves a problem of complicated control because stopping of replenishing the sub-tank unit with ink depends on the sensor.
A record head in which a pressure generation chamber is expanded and contracted by displacement of a piezoelectric vibrator involves the following problem: If air is solved in ink, bubbles easily occur in the pressure generation chamber, causing an ink drop jet failure to occur.
An ink jet recording apparatus of the invention comprises a sub-tank unit mounted on a carriage for supplying ink to an ink jet record head and an ink replenishment unit connected to a main tank installed on a housing by a duct and being able to be connected to and disconnected from the sub-tank unit, wherein the sub-tank unit comprises an ink injection port and an exhaust port that are communicated with an ink storage chamber via self-seal type valve means, and a valve mechanism for opening and closing the exhaust port based on a liquid level of ink, wherein ink is supplied to the ink storage chamber by negative pressure from negative pressure generation means for sucking air through the exhaust port.
According to the configuration, normally print is executed using ink in the sub-tank unit, and at the stage at which the ink in the sub-tank unit is decreased, the sub-tank unit is connected to the ink replenishment unit and pressure in the ink storage chamber is reduced for causing ink in the main tank to flow into the ink storage chamber. When the ink arrives at a predetermined level, flow-in of the ink is stopped by a float valve. The duration in the reduced pressure state can be prolonged to subject ink filled in the sub-tank unit to a degassing process.
It is therefore an object of the invention to provide an ink jet recording apparatus that can replenish a sub-tank unit with a predetermined amount of ink reliably in a short time regardless of the number of filling times with ink, and that can degas ink in the sub-tank unit as required.
It is another object of the invention to provide a sub-tank unit used with the ink jet recording apparatus.
It is another object of the invention to propose a method of recovering an ink droplet ejection capability of a record head of the ink jet recording apparatus.
The present disclosure relates to the subject matter contained in Japanese patent application Nos.:
Hei. 10-46315 (filed on Feb. 13, 1998);
Hei. 10-59078 (filed on Feb. 25, 1998);
Hei. 10-175341 (filed on Jun. 9, 1998);
Hei. 10-200377 (filed on Jul. 15, 1998);
Hei. 10-221137 (filed on Jul. 22, 1998);
Hei. 11-6600 (filed on Jan. 13, 1999);
Hei. 11-131141 (filed on Jan. 21, 1999);
Hei. 11-131142 (filed on Jan. 21, 1999); and
Hei. 11-13298 (filed on Jan. 29, 1999);
which are expressly incorporated herein by reference in their entireties.